A great concern has developed about release of toxic substances such as pesticides into the environment. Pesticides are of great importance for agriculture, but are hazardous and must often be disposed of in a manner that is environmentally acceptable.
An example is for greenhouses. A variety of plant species are grown in greenhouses where temperature and humidity may be controlled and the plants protected from environmental stresses. A variety of pesticides may be required for maintaining the health and vigor of the plants and preventing their destruction from any of a broad variety of organisms which may be damaging to the species being cultured. It is, therefore, not uncommon to introduce pesticides into a greenhouse by spraying the soil or foliage, or in gaseous form as a fumigant.
Since a greenhouse may remain relatively closed, the pesticides may persist and become a hazard to greenhouse workers. It may, therefore, be desirable to rinse floors, plants and other surfaces in the greenhouse to not only remove pesticides, but also to do the general clean up of leaves, twigs and the like which accumulate in a greenhouse. The water used for rinsing may often contain appreciable amounts of toxic material which should not be discharged into the open environment or ordinary waste disposal systems. Such rinse waters form dilute solutions of pesticides which are troublesome to dispose of. It is sometimes straightforward to substantially reduce toxicant concentration from a strong solution, as compared with the difficulty of removing relatively small amounts of contaminating toxicants from large volumes of dilute solution.
Further, when a greenhouse is fumigated it is eventually necessary to withdraw the toxicant laden air from the greenhouse. Thus, for example, a greenhouse may be fumigated in the evening and the fumigant permitted to remain through most of the night. Air circulation may be required, however, during the day to prevent the sun from overheating the greenhouse. It is desirable to prevent such air circulation from discharging toxic fumigants into the open environment.
Greenhouses are just one example of situations where fumigants or other pesticides may need to be disposed of. For example, food storage warehouses, transportation containers or truck trailers may from time to time require fumigation or similar treatment. Greenhouses, however, provide a good example for exposition of this invention. There are also a large number of greenhouses, each of which may discharge small amounts of toxic waste. Collectively these may have a substantial impact on the environment.
Such greenhouses may be relatively small scale operations so that costly waste treatment facilities would be uneconomic. It is, therefore, desirable to provide an inexpensive and ecologically safe alternative for present waste disposal systems, or more significantly to provide a waste disposal system where none may be presently employed.
It is desirable that the system be such that it can be readily scaled to the required size of the operation. Thus, for example, it is desirable that such a system be adaptable for use on a single greenhouse or for servicing a substantial number of large greenhouses occupying large plots of land. It is desirable that the decontamination system handle toxic wastes on site so that there is no need for transporting the wastes to remote locations. By completely degrading toxic byproducts on site, it is not necessary to export the problem elsewhere.
It is also desirable that the system be capable of handling both liquid and gaseous wastes so that, for example, the rinse water from a greenhouse and the fumigant withdrawn when air circulation is resumed may both be disposed of in the same system.
It is desirable to avoid "high tech" solutions which require great care in operation to assure continued satisfactory removal of toxicants. It is also desirable that the system be operable for removing a variety of toxic materials. This may be important since different pesticides are employed, depending on the season and stage of growth of various plant species and the types of pests that may adversely infest them.